This invention generally relates to vehicle wheels and more particularly to aircraft wheel configurations that increase the safety integrity of a wheel upon deflation of the mounted tire when rolling at high speed on a runway surface.
When a tire fails in a take-off or landing situation, the mating tire of a pair may also fail due to the increased and sometimes excessive loading to which it is subjected. When this happens, and the aircraft is moving at a high rate of speed, the tire carcasses eventually disentegrate resulting in the wheel flanges bearing directly against the surface of the runway. This situation has led to breakup of the wheels with parts being ingested into the engines and/or causing airframe damage and thus substantially increasing the hazard and possible loss of the aircraft.
In tests simulating a flat tire on an aircraft such as a Douglas DC-10, it was determined that when a cantilever-mounted wheel rolls without a tire, the inboard flange carries a major portion of the applied load. This is due to axle and/or wheel deflection, wheel stiffness, and/or the general wheel configuration. It was further determined that in an emergency involving a deflated tire, a wheel should be capable of rolling at least 3 kilometers (9,534 feet) without failure while carrying an applied load of approximately 0.95 percent of the maximum static load on the wheel resulting from maximum aircraft gross weight. For example, in the case of a Douglas DC-10 Series 30/40 aircraft, a wheel load of 57,000 lbs. may be experienced by a forged aluminum wheel weighing 212 lbs. It is imperative therefore, in an emergency situation, that each of the mounted wheels be capable of carrying the load irrespective of the inflated or deflated condition of a respective tire. This invention therefore, involves design analysis related to stress distribution in the wheel structure and deflection in the wheel and axle. These must be integrated with distribution of forces on the flanges such that the very low cycle fatigue endurance is balanced carefully between the two flanges.
It is the purpose of this invention to provide an aircraft wheel configuration that obviates the hazard of wheel fracture by providing greater structural integrity in the wheel without excessive additional weight. This allows the wheel to roll a substantially greater distance on the runway without breaking up. In this circumstance, an aircraft may come to a controlled stop even though the tires are deflated and it is rolling on the wheel flanges. In accordance with one aspect of the invention, an improved aircraft wheel is characterized by a differential flange height between the inboard and outboard flanges such that an increased outboard flange height exists to provide a substantially even distribution of the loading on the wheel flanges upon deflation of the mounted tire.
Various other objects and advantages of the invention will become evident from the description that follows when considered in conjunction with the accompanying drawings in the several figures in which like parts bear like reference numerals.